1. Field of the Invention:
This invention relates to a hydraulic die lifter unit for use in a pressing or punching machine. More particularly, the invention relates to a die lifter unit floatably fitted in the bolster of the machine, wherein the die lifter unit includes rollers adapted to allow a die to transport smoothly thereon, and also includes a hydraulic system for raising itself independently of the bolster.
2. Description of the Prior Art:
In a pressing or punching machine a molding or punching die is frequently dismounted from the bolster for replacement or repair, but because of its heavy weight, it is not an easy work, requiring a special tool, such as a crane. In order to lessen this toil, it has been proposed that the bolster be provided with a die lifter hydraulically floatable in a groove in the top surface of the bolster, wherein the die lifter has a plurality of rollers adapted to allow the die to roll thereon smoothly for dismount or mount. When the die lifter is raised under hydraulic pressure, the rollers rise up above the top surface of the bolster, thereby facilitating the transport of the die thereon. In this prior art die-lifter the hydraulic cylinder and oil path are provided within the bolster, which requires that the bolster is subjected to boring operation. However, as commonly known, the bolster is made of a thick metal block, and accordingly the boring is a difficult, expensive work.